Vacuum tube circuit



p 1940- R. J. KIRCHER 2,213,398-

, VACUUM TUBE CIRCUIT Filed July 22, 1938 2 Sheets-Sheet 1 IIQVVENTOII?a J. K/RCHER ATTORALEV Sept. 3, 1940.

VACUUM TUBE CIRCUIT Filed July 22, 1938 2 Sheets-Sheet 2 INVENTOR y RJK/RCHER ATTOkA/EK R. J. KIRCHER {2,213,398 v Patented Sept. 3;, 1940UNITED STATES PATENT OFFICE 2.213.398 VACUUM TUBE omoorr Raymond J.Kircher, Neptune; N. J., assignor to Bell Telephone Laboratories,incorporated, New

York, N. Y., a corporation of New York Application July 22,1938, SerialNo. 220,618

16 Claims. (01. 1'z9--1'r1.5)

This invention relates to vacuum tube circuits and moreparticularly'to'such circuits in which the interelectrode capacitybetween control grid and anode is or may be neutralized.

There is a need for a. simple, inexpensive circuit arrangement capableof use either for receiving or transmitting purposes.

condition is that the means used for one or the other purpose be usablefor the other with some simple change or readily operated control. Anobject of this invention is to meet this need.

A feature of the invention comprises using an electron discharge devicehaving inherent capac ity between its control electrode and its anode,

associating circuit means with such'electrodes so that the intrelectrodecapacity. is neutralized thereby preventing the occurrence of acondition of self-oscillation, and providing other means to alter theconstants of the neutralizing circuit whereby the device functions as anoscillator.

A further feature of the invention comprises connecting circuit meansbetween a pair of electrodes Of anelectron'discharge 'device andproviding relay means to change the characteristics of the circuitmeansto a desired extent, such relay means, for example, being manuallyor audio-frequency-operated or cont olled. Another feature of. theinveion comprises connecting circuit means between a pair of elec- 3' trodesof. anelectrondischargedevice, said circuit means including .a capacityelement provided by a second electron discharge device. A morecomplete-understanding of this inven- 'tion and its various featureswill be obtained from the detailed description which followshereinafter, taken in conjunction with the appended drawings, wherein: I

I Figs. 1 and 2 show vacuum tube circuits embodying the invention, f,Fig. 3 shows a vacuum tube transmitter circuit I embodying theinvention;

FigM shows a'combined transmitter and re-' ceiver circuit embodying. theinvention; and

Flgs..5 and 6 show electron c means for keying.

4 the neutralizing circuit of a vacuum tube,

The circuit of Fig. 1 comprises an electron p discharge device or triode[0 having a cathode -I I, a control grid l2, and an anode l3. A tunedcircuit I4 is connected to the grid-cathode and a second tuned circuitl5 is'connected across the cathode-anode. A source of grid biasingpotential and a source of plate potential are indicated. \The cathodemay be',.as shown, of the indirectly heated type. The numeral Itindicates the in- 55 herent capacity between the grid-and anodethat Apreferable;

per cent of that at which neutralization oc- ---of the circuit 28. maybe accomplished by the "tromagnet or relay 22 and battery 23 by closureof the contacts of key 24, armature 25 engaging causing condenser 2| tobe removed from the "26 being in engagement.

neutralizing circuit, whereby the tube ceases to signal input terminals40, is transformer coupled B, and to the neutralizing circuit controlcircuit may cause undesired oscillation of the device l0,

particularly when it is being used, for example, as adetector, anamplifier, ora demodulator. Various arrangements have been proposed to 5neutralize this capacity, and when high frequencies, for example, of theorder of hundreds of kilocycles or of megacycles, are involved,neutralizing by connecting an inductance between the control grid andanode has been found par- 10 ticularly efiective. In Fig. 1, theneutralizing circuit 28 is shown as comprising inductances l1, l8, avariable condenser I9, and a blocking condenser 20'. When the circuitsl4, l5 and 28 are tuned to the same frequency the vacuum 15 tube, as isknown, will not oscillate.

If either the reactive or capacitive constants of the anti -resonantcircuit between the grid and anode are altered, and allthe othercircuits remain unchanged, a condition of oscillation oc- 2o curs at afrequency that may be within a few curred. This alteration in the L or Cconstants connection of condenser 2| in shunt with con-. 25 denser IS oncompletion of a circuit for the elecvirithcontact 26 so long as the keyis operated. v The vacuum tube will oscillate until the contacts of key24 are opened, releasing armature 25 and circuit betweenthe grid andplate of the tube. Instead otthe tube normally being neutralized, itmay'normally be used as an oscillator with a '35 portionof theneutralization circuit shunted out as shown in Fig. 2, the armature 25and contact When it is desired to place the tube in condition for use,for example, as a detector. or asan amplifier, operation of the key toclose a circuit for. the electromagnet causes separation of the armatureand associated contact to place the inductance l1 effectively in thefunction'as an oscillator.

-' In Fig. 3, the invention is embodied in a signal wave transmissioncircuit. An audio frequency amplifier A, having suitable speech or otheraudio to the normally'neutraliz'ed vacuum tube circuit C. The amplifiermay be ofany suitable type and is shown by way of illustration as atwostage transformer-coupled amplifier embodying three electrode tubesof the indirectly heated 70 initial grid biasis provided by battery 15to give cathode type. The neutralizingcircuit so for the tube lcomprises an inductance 4|, a variable condenser 42, and blockingcondenser 20. The tuned circuit l5 comprises the output circuit for theneutralized vacuum tube and is coupled to the grounded antenna 43. Thecontrol 'circuit C comprises the relay or electromagnet 44, shunted by aby-pass condenser 45, in series with a rectifier 46, for example of thecopper-oxide type, and the secondary winding of amplifier outputtransformer 41. An armature 48, normally disengaged from its associatedcontact 49, is controlled by the electromagnet, and condenser 5|, uponengagement of the armature and associated contact, is adapted to beincluded in the neutralizing circuit to alter its constants to the endthat the tube is no longer neutralized and functions as an oscillator.In operation,

audio impulses are impressed on the input of the amplifier, and areamplified. A part of the amplied output is rectified by rectifier 46 tocause the control relay to close the circuit between the armature andassociated contact to alter, in pre- 4 determined manner, the constantsof the neutralizing circuit whereby the tube I 0 oscillates. The plateof the tube is simultaneously modulated by the amplified audio signaloutput and the modulated oscillator output is impressed on the antennaand radiated therefrom. Upon cessation of the audio signal input, theelectromagnet deenergi'zes, releasing the armature, and the tube I0 isreturned to its non-oscillatory condition pending arrival of furtheramplified audio signals.

The circuit arrangement .of Fig. 4 embodies the arrangement of Fig. 3,and includes means for receiving ordetecting an incoming signal duringthe neutralized condition of thetube, in which I period the tube l 0functions as a simple plate detector. The receiving means comprises atelephone headset 60 connected to thesecondary of the audio transformer6| whose primarywinding is connected'in the cathode circuit andby-passed A for radio frequencies. The neutralizing circuit 50 differsslightly from that of Fig. 3. Condenser 5| is connected in shunt tocondenser 42', the constants of the inductance 4 and the condensersbeing such'that the grid-to-plate capacity is normally neutralized,engagement of the armature 48 and contact 49 altering the circuit sothat the vacuum tube functions as an oscillator.

The circuits of Figs. 5 and 6 show electronic means for keying theneutralizing circuit of tube In. The input capacity of the controlelectron discharge device or triode 12 forms a part of the neutralizingcircuit of the tube l0 and is initially adjusted so that with theinductance 13 it neutralizes the inherent grid-to-plate capacity ii oftube ID. This .input capacity, as'is known, may be expressed in the formCFl+(}L|-1)cgp, where C3! is the geometrical capacity between controlgrid I4 and cathode l0, Cgp is the geometrical capacity between the gridand the anode II, and ,u is the effective voltage gain of the device 12.Variation of the biasing potential on the control grid 14 of tube 12causes a variation in the input capacity thereof, thereby altering theconstants of the neutralizing circuit a predetermined amount so as tocause the tube In to function as an oscillator. In the arrangement ofFig. 5, an

the initial desired input capacity. This initial bias may be changed toa desired degree by superwhich is connected in series with a source 11of low frequency current, for example, 1000 cycles per second, and anormally open key 1.8. 01', as

shown, in Fig. 6, the initial grid bias may be furnished by battery 80,the bias being changed to a. desired degree by closure of key 18 toeflfect a predetermined change in the input capacitywhereby theneutralizing circuit no longer functions to prevent tube' [0 fromoscillating. Coils 8|, 82, 83 are radio frequency chokes, condensers 84,85 and 86 are radio frequency by-pass condensers, and condensers 81, 88are blocking condensers.

Although this invention has been disclosed with reference to variousspecific embodiments, it is to be understood that it is to be consideredas limited in scope by the appended claims only.

What is claimed is;

1, In combination, an electron discharge device comprising a pluralityof electrodes and having such inherent capacity between a pair of saidelectrodes that it is capable of generating oscillations, meansrendering said capacity efiective to cause said device to generate.oscillations, means for neutralizing. the eflect of the capacity betweensaid electrodes, and audio frequency operated means for alteringsaid-second means so that said interelectrode capacity ceases to be.neutralized and said device will generate oscillations.

l 2. In combination, an electron discharge device comprising a cathode,a control grid and ananode, said device having an inherent capacitybetween said control grid and anode enabling it to generateoscillations, means rendering said capacity eifective to cause saiddevice to generate oscillations, an anti-resonant circuit connectedbetween said grid and anode for neutralizing the efiect of the capacitybetween said electrodes, and relay means for altering the constants ofsaid circuit to cause said capacity to cease to be neutralized and toenable said device to act as an oscillator.

' 3. In combination, an electron discharge device comprising a cathode,a control grid and an anode, said device having an inherent capacitybetween said control grid and anode enabling it anode, said devicehaving an inherent capacity between said control grid and anode enablingit to act as an oscillator, means rendering said capacity effective tocause said device to generate oscillations, an anti-resonant circuitconnected between said grid and anode for neutralizing the eifect of thecapacity between said electrodes, and audio frequency controlled relaymeans for altering the constants of said circuit to cause said capacityto cease to be neutralized and enabling said device to act as anoscillator.

5. In combination, an electron discharge devicecomprising a cathode, acontrol grid and'an anode, a tuned grid-cathode circuit, a tunedcathode-anode circuit, a tuned circuit across the grid and anode of saiddevice, said circuits being normally tuned to the same frequency wherebylay 2,21s,ees

any tendency for said device to oscillate because of interelectrodecapacity is neutralized, and means for modifying the constants of thegridanode tuned circuit to cause said device to os cillate.

6. In combination, an electron discharge device comprising a cathode, acontrol grid and an anode, a tuned grid-cathode circuit, a tunedcathode-anode circuit, a tuned circuit across the grid and anode of saiddevice, said circuits being normally tuned to the same frequency wherebyany tendency for said device to oscillate because of interelectrodecapacity is neutralized, and manually operated means for modifying theconstants of ,the grid-anode tuned circuitto cause said device tooscillate.

'7. In combination,-an electron, discharge device comprising a cathode,a control-grid and an anode, a tuned grid-cathode circuit,a .tunedcathode-anode circuit, atuned circuit-across the grid and anode of saiddevice, .said circuits being normally tuned to the same Irequencywhereby any tendency for said of interelectrode capacity is neutralized,and audio frequency operated means fol-modifying the constants of thegrid-arrode'tuned jcircuit to..

cause said device to oscillate;

8. In combination, an electrorf'discharge. de-

vice comprising a cathode, a control grid and an anode, a tunedgrid-cathode circuit, a tuned cathode-anode circuit, a tuned circuitacross the grid and anode of said device,' said circuits being normallytuned to the same frequency whereby any tendency for said device-tooscillate because of interelectrode capacity is neutralized, andregrid-anode tuned circuit to cause said device to oscillate.

9. In combination, vice comprising a plurality of electrodes, theinherent interelectrode capacity of said device being such that it maybeused' as a generator of oscillations, means renderingsaid capacityefi'ective to cause said device to generate oscillations,

circuit means includinganjnductance for neutralizing the effectof thecapacity between said electrodes, and audio frequency operated means forchanging said circuit means so that said capacity ceases to beneutralized andsaid device becomes a generator of oscillations.

10. In combination, an audio frequencyjamplig fier, an oscillationsgenerating vacuum tube circuit, means for neutralizing any tendency forthe vacuum tube to generate oscillations, means responsive to a portionof the amplifier output to modify the characteristics of saidneutralizing means so that the vacuum tube generates oscillations, andmeans connectingsaid amplifier and said circuit for modulation of theoscillations in accordance with the amplifier output.

11. In combination, an electron discharge dedevice tooscilla'te becausemeans for modifying the constants of the an electron dischargedecapacity vice comprising a plurality of electrodes, means ;co nnecteddirectly between a pair of said electrades for neutralizing the efiectof capacity between said pair of electrodes, said means includ-.

' trodes for neutralizing the efiect of capacity between said pair ofelectrodes, said means including an electronic device providing acapacity element in said means, and means individual to said electronicdevice for adjusting'the capacity of said capacity element.

13. In combination, an electron discharge device comprising a pluralityof electrodes and having a tendency to oscillate because of inherentinterelectrode capacity, circuitmeans for neutralizing said tendency,said means including an electron discharge device having a plurality ofelectrodes, theinterelectrode capacity between which provides a capacityelement in said neumeans'including .a space discharge device comprisinga' control grid, a cathode and an' anode,

the inputcapacity of said second device being a capacity element in saidcircuit means, and

means for changing the bias on the second devic'es control grid tochange said input capacity a predetermined amount so that the firstdevices oscillation tendency is no longer neutralized.

15. In combination, an oscillations generating electron dischargedevice, said-device comprising tralizing means, and means for changingthe a control grid, a cathode and an anode, circuit means includinginductance and capacity elements connected between the grid and anode,.

means for impressing a modulating signal input on said device, and relaymeans for changing the constants of said circuit means to a predetermined extent, said relay means being responsive to a portion of theinput to said device.

- 16. In combination, an electron discharge-device comprisinga controlgrid, a cathode and an anode, circuit means'including inductance andelements connected between the grid and anode, and audio frequencyoperated relay means for changing the constants of said circuit means toa predetermined extent. 1

